Positraction Diff I.D.

[Guest imported_bjr]

I have a GM posi unit I am trying to identify. The following numbers are cast into the carrier: F185, EDB 30162. Stamped on the carrier is: G2F6. It has a 8.75" diameter 41 tooth ring gear, with the following stamped on the ring gear: 4116 GM 7650. The ring gear has 12 bolts that hold it to the carrier. The axles are 31 spline and 1.3125 diameter. If anyone has a parts book or can ID this it would much appreciated. I believe it's from the early 1970's. Thanks Brian

[Guest imported_bjr]

Doen't anyone have a parts book or some info on this?

[NTX5467]

Unfortunately, the GM parts books back then typically had no mention of casting numbers or other similar numbers. I have observed that typically, the gear ratio of the particular matched set of ring gear and pinion are stamped on the outer edge of the ring gear. I suspect the "4116" number would actually be 41 teeth on the ring gear and 16 teeth on the matching pinion gear, yielding a 2.56 gear ratio. The other stamped numbers on the edge of the ring gear would be other related production codes, but I haven't seen that they are decodeable in the GM parts books.

In those earlier times, the axles were usually identified visually (Chevy, Olds, Pontiac, etc.) by the shape and number of bolts holding the rear cover plate to the axle housing. There are also stamped numbers on the passenger side axle tube (usually about half way between the center housing and the brake backing plate, on the front side) that basically is the birth certificate for the axle assembly--with information that can be decoded in the GM parts book section on that subject.

Usually, the diameter of the axle shaft and the number of splines is not mentioned in the GM part books either, unless there might have been a design change during a particular model year. The place where that information could be pertinent would be with the aftermarket drag racing axle people who usually key on those particular specs in building replacement axles for specialized racing applications.

Several years ago, a friend had a need for information on a Dana-manufactured axle that no one had any information on. Local parts suppliers said "Check the dealer" and the dealer was similarly uncooperative. He finally found a Dana jobber that was interested in supplying him or telling him where to find the desired manuals on each rear axle or front axle they built at that time, plus vehicular application data. It took some tenacious doing, but he did it. Unfortunately, I have doubts that a similar manual could be obtained for any GM rear axle that was not a Dana-supplied unit. Anyone know of any similar strings that could be pulled with respect to GM specification non-Dana rear axles? Maybe some old "Advance Information" service manuals or maybe particular years of GM service manuals?

I suspect that unless someone in the muscle car racing area or there exists some archived engineering data somewhere, it might be difficult to accurately ID the carrier with the information supplied. Of course, it might be possible to "go in through the back door" by possibly checking the side bearing mounting area diameters and getting into a comprehensive automotive bearing book that had those specs and then comparing them to bearings that GM spec'd for particular applications in the 1970s. Then cross-reffing that information with the ring gear diameter and gear ratio might get you into some "window" of possible applications.

Hope this helps,

NTX5467